5 Fascinating Facts about Twins

Seeing double? This year American women will give birth to more than 140,000 sets of twins. Here's what you need to know about these compelling carbon copies.

By Taylor Shea
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    To tell twins apart, look at their...

    ...belly buttons! Navels are scars from the detachment of the umbilical cord after birth, so they aren't caused by genetics. Another way to determine who's who: Take fingerprints. Identical twins may share DNA, but exposure to different areas of the womb during development affects the fingertips' ridges and whorls.    

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    Twins can be conceived by two different fathers

    Heteropaternal superfecundation occurs when a woman has sex with more than one man during ovulation. Sperm from each man fertilizes an egg, resulting in twins. Though this phenomenon is common in dogs and cats, it's extremely rare in humans.  


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    The chance of having twins is much higher than it was 30 years ago

    The birthrate for twins has increased 76% since 1980, an uptick that some experts attribute to older women having children (women in their thirties are more likely than women in their twenties to have twins). Or maybe women are getting taller: A Long Island Jewish Medical Center study found that women who birth twins or other multiples were, on average, more than an inch taller than women who only birthed one child at a time. 

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    Fetuses that share a womb and a birthday aren’t necessarily twins

    An extremely rare condition called superfetation occurs when a pregnant woman continues to menstruate and a second embryo forms. Often, the fetus conceived last is born prematurely, while the fetus conceived first is carried to term, but in some cases, the babies are born on the same day.  

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    Twins speak their own language

    What sounds like kids' babbling could actually be cryptophasia, a language developed between twins that only they can understand. Research published in the journal Institute of General Linguistics found that twin babies often use each other to learn vocabulary. The research estimates that up to 40 percent of twins create a private language.